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Research Project: Genetic Improvement of Small Grains for Biotic and Abiotic Stress Tolerance and Characterization of Pathogen Populations

Location: Plant Science Research

Title: Tissue-specific gene expression in maize seeds during colonization by Aspergillus flavus and Fusarium verticillioides

item SHU, XIAOMEI - North Carolina State University
item Livingston, David
item FRANKS, ROBERT - North Carolina State University
item BOSTON, REBECCA - North Carolina State University
item WOLOSHIK, CHARLES - Purdue University
item PAYNE, GARY - North Carolina State University

Submitted to: Molecular Plant Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/2/2014
Publication Date: 2/4/2015
Citation: Shu, X., Livingston, D.P., Franks, R.G., Boston, R., Woloshik, C., Payne, G.A. 2015. Aspergillus flavus and fusarium verticillioides induce tissue specific gene expression of PRms and UGT in maize kernels. Molecular Plant Pathology. 16:662-674.

Interpretive Summary: Two fungi that infect corn kernels are Aspergillus flavus and Fusarium verticillioides. These 2 fungi produce micotoxin in infected seeds and are therefore very dangerous to both humans and animals. It has been difficult to design a strategy to control these fungi because how they interact with their host is very poorly understood. In this study the means by which the fungi colonize the seed and the genes that are produced by the seed to oppose infection were monitored and imaged using light microscopy. Analysis of images indicated that both fungi followed a similar pattern of infection. The pattern of gene expression however differed in the 2 fungi and the 2 genes followed were expressed before the presence of the fungus was visualized. This study indicates that the pattern of colonization by the fungi is predictable and that the technique used here can be used to follow the expression of defense genes by the plant giving breeders better insight in designing strategy to control infection.

Technical Abstract: Aspergillus flavus and Fusarium verticillioides are fungal pathogens capable of colonizing maize kernels and contaminating them with mycotoxins. Development of effective control strategies is extremely difficult because pathogenesis and host response remain poorly understood. In this study, we monitored colonization and host tissue-specific gene expression during infection by these two fungi. Immature maize kernels were inoculated with either A. flavus or F. verticillioides 21-22 days after pollination. Kernels were harvested at 4, 12, 24, 48, 72, 96, and 120 hours post inoculation (hpi). Histological studies showed that the two fungi followed a similar pattern of colonization. RNA in situ hybridization showed that transcripts of maize pathogenesis-related protein, maize seeds (PRms) were detected in the aleurone and scutellum during infection. However, transcripts of maize shrunken-1 (Sh1) were observed in the embryo before fungal infection, and this gene was induced in the aleurone and scutellum during infection by both fungi. By comparing histological and RNA in situ hybridization results from adjacent serial sections, we found that these two genes were expressed before visible colonization. These studies show a predictable pattern of colonization by two seed infecting fungi and indicate that RNA in situ hybridization can be used to follow temporal and spatial expression of defense genes in maize kernels.